Pulverized fuel burner



Patented Dec. 23, 1941 NITED STATES PATENT OFFIE 4Claims.

The invention relates to pulverized fuel burners, and more particularly to burners of this character suitable for use in domestic or other small heating systems.

A general object of the invention is to provide an improved pulverized fuel burner of the above general character'which, by reason of its simple, sturdy construction, relatively low cost, and eflicient and reliable operation, is particularly suitable for use in domestic heating systems.

Another object is to provide a pulverized fuel burner embodying a nozzle of improved construction adapted to promote rapid ignition and complete combustion of the pulverized fuel.

Another object is to provide improved means for introducing secondary air into the burner to insure complete and intimate mixture of the fuel and air.

Another object is to provide an improved igniter for pulverized fuel burners which can be installed with a minimum of labor and which can be quickly and easily removed and replaced when necessary.

It is also an object of the invention to provide a novel method of burning finely pulverized fuel which enables this type of fuel to be utilized in domestic heating systems.

Other objects and advantages of the invention will become apparent from the iollowing detailed description of the preferred embodiment illustrated in the accompanying drawing, in which:

Figure 1 is a central vertical sectional view of a pulverized fuel burner embodying the features of the invention.

Fig. 2 is a fragmentary plan view of the burner.

Fig. 3 is a sectional view taken along the line 3-3 of Fig. 1 showing the relationship of the fuel and secondary air orifices.

Fig. 4 is a sectional view taken along the line 4-4 of Fig. 1 showing details of the igniter.

By way of illustration, the invention has been shown and will hereinafter be described in connection with a steam or hot water heating plant of the type commonly used for domestic heating. It is to be understood, however, that the invention is not limited to the particular form or environment shown and that various modifications, adaptations and alternative constructions may be resorted to without departing from the spirit and scope of the invention as expressed in the appended claims.

Referring to the drawing, the burner constituting the exemplary embodiment of the invention is shown in connection with a steam or hot water heater having a boiler 5 with an inner shell 8 defining a vertical, conically tapered combustion chamber I. The combustion chamber is provided with a refractory lining 8. A combustion ring 9 of refractory material forms the upper wall of the combustion chamber and the lower wall of an air chamber II! from which secondary air is supplied for thecombustion of the fuel within the chamber I.

The air chamber In is closed at its upper end by a casing ll having a removable top or cover l2. The casing II is generally V-shaped in horizontal cross section and rounded at its larger end (see Fig. 2) to fit tightly upon the upper end of the boiler shell 6. The smaller end of the casing projects laterally over the top of the boiler to receive a secondary air duct 13 through which air under low pressure is supplied by a suitable blower (not shown). The connection between the duct 13 and the casing II is made by way of a branch duct l4, leaving the end of the duct is open to provide a relief outlet for gases and thus prevent building up of excessive back pressures in the blower system due to pulls or small explosions which may occur in the combustion chamber when the burner is initially started. The open end 01 the duct is closed by a relief door l5 hingedto a collar l5 encircling the duct. The weight of the door is sumcient to maintain the relief outlet closed under normal operating conditions.

The various elements of the burner structure are assembled in a compact unit and mounted within the secondary air chamber l0. As shown in Fig. l, the burner comprises a pulverized iuel nozzle 2! arranged to discharge downwardly into the combustion chamber 1 through the opening in the combustion ring 9. The nozzle in its preferred form consists of a generally conical hollow casting the walls of which taper gradually to a point approximately midway of its length and then flare outwardly as at 22 and merge into an enlarged cylindrical end portion 23; The outside diameter of the end portion 23 is such as to leave an annular opening communicating between the combustion chamber 1 and the secondary air chamber 10. This opening constitutes the orifice through'which secondary air is "supplied for combustion oi the fuel discharged through the nozzle.

The nozzle 2| is preferably supported from the cover plate [2 so as to avoid placing unnecessary strains on the combustion ring and the refractory lining of the combustion chamber. To this end, the nozzle is formed at its upper end with an annular flange 25-adapted to be bolted or otherwise secured to the cover plate in registration with an aperture 23 which forms ae forafuelfeedpipe.

The fuel feed pipe, as herein shown, consists of'a tapered elbow 21 having its enlarged end formed with an annular flange 28 adapted to be bolted to the flange 25 of the nomle. The other end of the elbow is supported by upstanding nozzle. The mixer, as herein shown, comprises a metal plate 3| adapted to be clamped between' the flanges and 28 of the nozzle and elbow.

The area of the plate 3| within the nozzle is a formed with an outer row of inclined'vanes 32 and an inner row of oppositely inclined vanes 33 which divide the air and fuel mixture into a series of oppositely moving streams and thus insure the proper mixture of the fuel and air.

The fuel and air mixture delivered to the nozzle is discharged into the combustion chamber I in a manner such as to facilitate rapid ignition and complete combustion of the fuel in the combustion chamber. To this end, a spreader 36 is supported in the enlarged lower end of the nozzleby means of a rod 31 anchored in a boss 38 formed integrally with the elbow 21. As herein shown, the spreader comprises a hollow sheet metal shell having a generally conical top 39 and a substantially cylindrical body portion 40. The shell which is preferably open at its lower end may be filled with a suitable refrac-. tory material 40 to protect the metal parts from the heat of the combustion chamber.

The body portion 40 of the spreader is of sub stantially less diameter than the cylindrical lower wall 23 of the nozzle. When the spreader is centered in the nozzle, as shown in Fig.1, it thus defines with the wall 23 an annular fuel orifice 4| concentric with the secondary air orifice.

The particular form and relationship of the orifices is of extreme importance in obtaining complete combustion of the fuel and in effectu ally eliminating coking or the deposit of unburned or partially burned fuel on the walls of the combustion chamber. The secondary air enters the combustion chamber in a hollow cylindrical stream surrounding the hollow cylindrical fuel and air stream which is of relatively large diameter. 'Moreover, the fuel and air stream is defined by a relatively thin wall of primary air and entrained fuel particles so that the, fuel particles are quickly heated to combustion temperature by radiation from the burner flame and from the combustion chamber walls. Since the fuel and primary air stream is closely 'encircled by the cylindrical secondary air stream,

the fuel particles are quickly dispersed through the secondary air stream which supports combustion.

This novel method of introducing-the pulverized fuel and air into the combustion chamber in thin walled, relatively large diameter concentric hollow cylindrical streams enables such fuel to be used satisfactorily in the relatively small combustion chambers available in domestic heating plants. Relatively low pressures may be employed, thus producing a soft flame which has no tendency to erode the walls of the combustion chamber. Moreover, complete combustion takes place in the upper end of the combustion chamber close to the burner so that coking or the deposit of carbon on the walls or burner parts is effectually avoided.

Rapid mixing of the fuel particles with the secondary air stream is facilitated and stratification of the air is prevented by the provision of means for imparting a' rotary motionto the secondary air stream. This means, as herein shown, comprises a series of vanes 45 formed on the inner surface .of an annulus 45 disposed within the opening of the combustion ring 9. As will be seen by reference to Fig. 3, the vanes 45 are inclined at an angle to the axis of the air orifice and therefore deflect the various components of the air stream from a vertical path. The annulus is supported on the combustion ring by means of a flange 41. Laterally projecting flanges 48 on the nozzle 2| bear against the flange 41 and prevent displacement of the ring when the burner is in operation.

Ignition of the pulverized. fuel is effected by means of an igniter which, as herein shown, includes a pilot. tube 5| arranged to project a gas flame through the secondary air orifice and into the combustion chamber 1. The pilot tube 5| is removably mounted in a generally vertical bore 52 formed in a boss 53 integral with the side wall of the nozzle. The bore 52 is preferably of generally oval cross section, thereby providing an air inlet for the pilot flame in addition to accommodating th pilot tube itself. As herein shown, the pilot tube 5| is supported in the bore 52 by means of laterally projecting lugs 54 engaging in longitudinally extending grooves 55 formed in opposite walls of the bore. Thus, the pilot tube may be readily assembled with the burner or removed for replacement or repair. A flexible pipe or tube 55 connected with the upper end of th pilot tube by means of a coupling 56 supplies gas to the pilot burner.

Ignition of the pilot burner may be effected in any suitable manner as by a hot wire igniter 51 of usual and well known construction. The igniter 51, as herein shown, is in the form of a tight coil of resistance wire mounted in a suitable holder 58 slightly below the lower end of the pilot tube 5|. A'shield 59 secured to the boss 53 and extending downwardly to the vane supporting flange 41 prevents the pilot flame from being extinguished by eddies in the secondary air chamber.

It will be understood that any suitable system of controls may be employed for controlling the operation of the burner. Such controls are old and well known in the art and are therefore not shown in detail. In general, it may be stated that the controls are so arranged that the secondary air blower is startedand current is supplied to the igniter 51 upon a call for heat from the burner. After a predetermined delay sufficient to allow the igniter to reach the desired temperature, a valve in the gas pipe 55 isv opened The gas flowing from the Pilot tube a over the heated coil is ignited and forms a pilot flame which is projected into the combustion chamber. Simultaneously with the opening of the gas valve, the fuel feed blower is started and fuel and air mixture is discharged through the.

burn until the combustion chamber heats up sufficiently to ignite th fuel, whereupon the pilot flame is extinguished.

It will be apparent from the foregoing that the invention provides a pulverized fuel burner of metal ring supported on said combustion ring simple and sturdy construction which is efiicient and reliable in operation and particularly suitable for use in domestic heating plants. The burner embodies a nozzle of novel and advantageous construction arranged to discharge a primary fuel and air mixture into the combus- 1. In a pulverized fuel burner for use in aver-- tical combustion chamber, a combustion ring having a circular opening supported at the top of the combustion chamber, a nozzle having one end disposed in said opening and coacting with said ring to define an annular orifice for discharging a hollow cylindrical stream of secondary air into the chamber, means cooperating with said nozzle toform an annular fuel orifice concentric with said air orifice for discharging a hollow cylindrical stream of primary air and entrained pulverized fuel into the combustion chamber, a metal ring supported on said combustion ring and encircling said air orifice, and a series of vanes formed around the inner edge of said metal ring, said vanes'being inclined relative to the axis of the ring and disposed within said air orifice and operative to produce axial rotation of the secondary air stream relative to the stream of primary air and pulverized fuel discharged through the fuel orifice.

2. In a pulverized fuel burner for use in a vertical combustion chamber, a combustion ring having a circular opening supported at the top of the combustion chamber, a nozzle having one end disposed in said opening and coacting with said ring to define an annular orifice for discharging a hollow cylindrical stream of secondary air into the burner, means cooperating with said nozzle to form an annular fuel' orifice concentric with said air orifice for discharging a hollow cylindrical stream of primary air and entrained ,tion chamber in the form of a hollow cylindrical and encircling said air orifice, a series of vanes formed around the inner edge of said metal ring and positioned in said air orifice, said-vanes being inclined relative to the. axis of the orifice to impart a rotative movement to the secondary air stream, and means formed integrally with said nozzle for holding said metal ring in fixed position.

3. The combination with a pulverized fuel burnerfor use in a vertical combustion chamber,

' said burner having a secondary air chamber disposed above the combustion chamber and opening into the same and a fuel nozzle mounted in said air chamber with its discharge end positioned in the opening to define concentric air and fuel orifices for the discharge of fuel and air into the combustion chamber, of means for igniting the fuel including, a gas pilot tube, a bracket formed integrally with the nozzle having a bore of generally oval cross section, said bore, having grooves formed in the opposite walls thereof and being adapted to receive the tube, and flanges on said tube cooperating with said grooves in,

said bore to removably hold the pilot tube at one side of the bore substantially parallel to the axis of the air orifice and in communication therewith, said bore forming at its other side a duct for supplying air to support the combustion of gas discharged from the pilot tube.

4. In a pulverized fuel burner for use in a vertical combustion chamber, the combination of a combustion ring having a circular opening located at the top of the combustion chamber, a metal annulus disposed in said opening and having an outwardly projecting circumferential fiange seated on the combustion chamber, an elongated frusto-conical fuel nozzle having an annular orifice at its larger end and connected at its smaller end with a fuel feed line, means for supporting the smaller end of the nozzle above and substantially coaxially of the opening'in the combustion ring with the larger end thereof disposed in said annulus to define therewith a second annular orifice concentric with the first I orifice, and means for positioning said larger end of the nozzle with reference to said annulus including radially projecting flanges on the nozzle shaped to extend over said annulus and tomoperate with the flange thereof, said radial flanges additionally acting to hold the annulus against movement relative to the nozzle.

AUBREY J. camnm'.

pulverized fuel into the combustion chamber, a 

